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The term “roof vent” can mean many things. As we define it, a roof vent is designed to remove hot air and moisture out of your attic.
There are many different types of roof vents that accomplish this task in different ways. Some are motorized, powered by electricity and wired into the home, some utilize solar cells, some are powered by wind and others require nothing at all. This leads us to the most common question we are asked concerning roof vents…
Anyone who states flatly that one vent system is superior to another does not understand the real issue. See, what is so critical to understand is that not all homes are designed the same way and are not exposed to the same climate; therefore not every home is best served by the same ventilation options. The BEST roof vent for your home is the one that factors in your home’s airflow and roof’s design to remove the most cubic square footage of attic air space the most effectively. So to answer this question, find an unbiased roofing contractor who will design a custom ventilation system for your home.
A common rule across most residential building codes calls for 1 square foot of vented area for every 300 square feet of attic space with a vapor barrier and 1 : 150 without a vapor barrier. This means a 1,500 sq. ft. attic (with vapor barrier) should have 5 sq ft of vent space. Half of this is to be dedicated for air intake in the soffits (soffit vents) and the other half for exhaust through the roof.
Box Vents also called Low Profile Vents, Louvers, Flat Vents, or Turtle Vents are static vents. This means they have no moving parts. The vent is installed over a hole cut out of the roof. Utilizing natural convection, they create an opening for the rising hot air and moisture to escape through. They are available in different colors as well as both metal and hard plastic. Box Vents are most effective when installed as close to the roof ridge as possible. This allows the maximum amount of heat and moisture to be released. Due to their limited effectiveness numerous Box Vents are often required.
Also called whirlybirds. These vents are not static, as they have moving parts, but they do not have motors and instead rely on the wind to power their movement. A lot of people see a wind-driven turbine vent and think of a Chef’s hat. Wind-driven turbine vents move more air than box vents – when the wind is blowing. They are available in differing degrees of quality. We recommend only installing high quality wind driven turbine vents that have plastic bushings or permanently lubricated ball bearings in the spinning mechanism. Most homeowners are familiar with the squeaking noise associated with the cheaper versions as they spin in the wind. It’s that spinning action, triggered by wind, which draws hot air and moisture up out of the attic.
Power ventilators (roof or gable mounted) also known as PAVs (Power Attic Vents) have motors that turn large fans to drive hot air and moisture out of the attic. They are available in a variety of colors. Some come equipped with adjustable thermostats which trigger the fan to kick on when the attic reaches a certain temperature. They are also available with a humidistat that will detect levels of humidity and turn on. It goes without saying that power ventilators require electricity to operate. Most are hardwired into the house’s electrical, however there are models with built in solar panels to power the unit. These units are designed to function relatively quietly and do a good job of venting. One downside we often encounter is that a power vent can be dead but due to its quiet design homeowners may not realize it no longer functions. For this reason we recommend a quick inspection of the unit every six months.
Testing has demonstrated photovoltaic (solar) power vents can reduce peak summer attic air temperatures by over 20 degrees Fahrenheit. Unfortunately, while cooling the attic power vents often accomplish this by pulling conditioned air up out of the house – through the attic access, light fixtures, wiring penetrations through the top plates in walls, and any other path air can find. This often results in the inability to properly cool the interior of the home, as conditioned air is quickly expelled. Consequently, Power Vents are considered costly.
Ridge vents are a static vent system – with no moving parts. Imagine a book opened and laying face down. The book’s spine would be the ridge on a roof that you would install ridge vent. A ridge vent should run the entire length of the roof’s horizontal ridge, blending into the roofline for a more attractive home. We often see where roofers did not run the ridge vent from end to end and this creates an unfinished look. Ridge vents combined with undereave venting (soffit) is the most efficient system you can install. While other forms of ventilation create hot and cold zones on the roof’s surface, ridge vent provides even distribution of temperature. This means sections of the roof are not aging faster than others. Ridge vent is not dependent on wind, so changes in wind speed and direction have no real significant effect on performance.
Often confused with box vents, Off Ridge Vents function similarly. They are static vents placed over a cut section in the roof near the ridge. Rather than being square like a box vent, they are long and thin. While they allow hot and moist air out of the attic space, they are typically not the most effective, requiring several units.
Cupola vents are often purely decorative, however they can be functioning static roof vents. They sit atop a high ridge and frame an opening in the roof system, allowing hot air and moisture to rise and escape the building envelope. While they can be a functioning roof vent, they are limited in their abilities and usually fill a support role to another primary roof vent system.
Last but certainly not least are Soffit Vents which provide a means of air intake into the roof’s ventilation system. They are installed in soffits and eaves and most often made of PVC or aluminum. If your home is fitted solely with small gable-end vents or only vents in the roof, you should consider installing soffit vents to increase airflow. Allowing outside air to enter the attic at the lowest point of the roof, soffit vents are most effective when used in conjunction with a continuous ridge vent.
This article was originally published by Sparrow Exteriors, a home improvement contractor serving Greater Atlanta Georgia.